RFR: 8289743: AArch64: Clean up patching logic [v12]

[Andrew Haley]

> The current logic for patching is a mess of if-then-elses. By rearranging the logic and using a switch we can make it both easier to understand and faster.

Andrew Haley has updated the pull request incrementally with two additional commits since the last revision:

 - 8289743: AArch64: Clean up patching logic
 - 8289743: AArch64: Clean up patching logic

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9398/files
  - new: https://git.openjdk.org/jdk/pull/9398/files/12556196..7b647d17

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9398&range=11
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9398&range=10-11

  Stats: 29 lines in 1 file changed: 10 ins; 2 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/9398.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9398/head:pull/9398

PR: https://git.openjdk.org/jdk/pull/9398